Recently, porphyrin derivatives which are in a liquid form at ambient temperature were developed (see, for example, Patent Literature 1). Patent Literature 1 discloses porphyrin derivatives represented by the formula shown below:

According to Patent Literature 1, in the formula shown above, M denotes an atom or a compound capable of forming a covalent bond or a coordinate bond with 2H (hydrogen atoms) or tetraphenyl porphyrin. Each of R1, R2 and R3 denotes, independently from each other, a hydrogen atom, or an alkoxy group having 7 to 15 carbon atoms represented by OR4, R4 is a substituted or unsubstituted alkyl group having 7 to 15 carbon atoms, identical meanings are applicable within all R1s, all R2s and all R3s, respectively. Each of R2 and R3 is an alkoxy group having 7 to 15 carbon atoms represented by OR4 and R1 is a hydrogen atom, or each of R1 and R3 is an alkoxy group having 7 to 15 carbon atoms represented by OR4 and R2 is a hydrogen atom, or each of R1 and R2 is an alkoxy group having 7 to 15 carbon atoms represented by OR4 and R3 is a hydrogen atom, or, each of R1, R2 and R3 is an alkoxy group having 7 to 15 carbon atoms represented by OR4.
Since the porphyrin derivatives in Patent Literature 1 have 3 to 5 alkoxy groups having a certain number of the carbon atoms in a certain position on the phenyl ring, they have a liquid property at room temperature (25° C. to 40° C.) without containing any solvent and also have a high thermostability.